1. Field of the Invention
The art to which this invention relates concerns impact printers of various kinds including train, chain, band and drum types. More particularly, it relates to means for electronically adjusting the spacing between columns of print produced by impact printers.
2. Description of the Prior Art
Known impact printers employ a moving character font which passes by a number of print hammers at a constant velocity which, typically, is of the order of 200 inches per second. Print hammers positioned opposite to the type font are electronically activated on a selected basis by high energy pulses to impel them momentarily in a direction which causes their faces to impinge on the type font. Ribbon and paper located between the type font and the hammer heads enables the transfer of images from the type font to the paper as the hammer heads are actuated.
Due to differences in the actual operating characteristics of the print hammers, it is necessary to provide means to adjust the hammers to enable proper column-to-column spacing on the resulting printouts while assuring that the proper energy is delivered by the hammers. Possible adjustments to provide proper intercolumn spacing include changes in the power stroke to the hammer and in the spacing between the hammers and the type font.
The power stroke of each hammer is produced by a fire pulse which determines the energy level with which the hammer strikes the font. The fire pulse producing the power stroke, though having an effect on spacing between printed columns, has not been treated in the past as a means of varying the spacing between the printed columns.
Mechanical adjustments in the hammer position relative to the character font, i.e. adjustments in the spacing between the hammers and the character font have been commonly relied upon as the sole means of adjusting the column-to-column spacing once the basic manufacturers tolerances have been established. In the course of manufacturing the printer this involves making manual final adjustments in spacing between the hammers and the type font within certain tolerances. When the printers are in commercial use, adjustments to correct any errors which develop in the spacing between columns involves changing the spacing between the striker tips of individual hammers and the faces of the character fonts. In practice this requires the removal of covers on the printing machine, the release of screws holding selected hammers in place, selected movement of the hammers, retightening of the screws, and replacement of the covers. The process is tedious and may consume several hours of valuable time under adverse circumstances. Just how tedious will be better appreciated when it is realized that a mirror is necessary in many instances to enable a maintenance person to see some of the parts which must be adjusted.
Reference may be made to FIG. 1 for further details of the prior art which are believed to be useful to understanding the present invention. It will be seen that FIG. 1 illustrates a prior art hammer of a kind used in printing machines to which the invention relates.
The hammer includes a frame at 2 which supports a coil and core at 4. The coil is energized by pulses through wires 6 and 8 to drive an armature 10 which is hinged at 12. An interposer 14 is supported by flexures 16 and 18 enabling a hammer face 15 on interposer 14 to be driven against a layer of paper 17 which in turn impinges against an inked ribbon or carbon 19 and a character font to form a character on the paper. A screw assembly at 20 is used to limit the travel of the armature 10 and control the force it can apply to the interposer 14 thus assuring that a satisfactory image is produced on the paper.
Adjustment of the spacing between characters, which are printed by interaction of the hammer and character fonts, is controlled chiefly in the prior art by releasing screws at 22 and 24 and adjusting the screw at 26. When the screws at 22 and 24 are loosened, permitting their shafts to be moved up and down within elongated slots at 25 and 27, it is possible to move the hammer assembly up and down relative to the hammer support base 28. This up and down movement varies the spacing between the hammer face 15 and the paper at 17 and thus the timing of the impact causing a character to form on the paper. The position of a character on the paper will be shifted in position in a direction and by an amount determined by this adjustment.